The correct answer is - interplate tectonic setting.
The Yellowstone National Park is located in close proximity to a plate boundary. This makes this place geologically very active, with the numerous gazers, volcanoes, earthquakes, faults, in the surrounding area witnessing about it.
The igneous activity is due to the penetration of the magma from the mantle layer towards the surface. Since it is a plate boundary in question, there's cracks in the crust, and the magma manages with relative ease to reach the surface, coll down, and create new igneous rocks.